Abstarct: The purpose of this research was to investigate the effect of competitive anxiety on sports burnout with the role of moderator of mental toughness of high school students. The method of the current research was descxriptive-correlative in nature and cross-sectional in terms of time. The statistical population of the research was all the sports students of the second secondary level of Bojnord city, and 273 people were selected as a sample using random-cluster sampling method. The research tools were the three standard competitive anxiety questionnaires of Cox et al. (2003), Raedeke and Smith's sports burnout questionnaire (2001) and Dagnall et al.'s (2019) mental toughness questionnaire. Structural equations with variance-oriented approach were used to check the research hypotheses. SPSS23 and Smart-PLS 3.2.8 software were used for data analysis in the present study. The results of the research showed that competitive anxiety has a direct and significant effect on sports burnout, and in the relationship between competitive anxiety and sports burnout, the mental toughness variable has a (negative) moderating role. According to the results of the research, it is suggested that coaches, physical education teachers and other officials should reduce their competitive anxiety and prioritize the development and strengthening of mental toughness by holding educational workshops in order to reduce their sports burnout